Perhaps channeling the late Liberace himself, Sharon Stone was a red-carpet diva at the premiere of Steven Soderbergh’s biopic on the primping piano man yesterday. Stone showed up to the premiere of “Behind the Candelabra” in Cannes wearing a Roberto Cavalli gown with a plunging neckline, and outshined the movie’s male stars Michael Douglas and Matt Damon. But Stone, spies said, also committed a Cannes faux-pas by entering the theater at the Palais des Festivals after the film’s director and cast — causing some snickering in the aisles. “Sharon got laughs from the crowd inside the theater at the premiere because she showed up on the red carpet after the cast and director had already made it through and inside . . . that’s a no-no here!” Last night, Stone showed off another bombshell dress that revealed many of the body parts that weren’t exposed at the “Candelabra” screening. This time she wore a backless (and left side-less!) red number with a sky-high slit to de Grisogono’s party at the Hotel du Cap Eden-Roc, where guests included Harvey Weinstein, Paris Hilton, Chris Tucker, Vladimir Restoin Roitfeld and Tamara Ecclestone.